Segmented electron shield for color picture tube

ABSTRACT

AN ELECTRON SHIELD FOR A SHADOW-MASK TYPE OF COLOR TUBE BRIDGES THE SPACE BETWEEN THE MASK FRAME AND THE TUBE ENVELOPE. THE ELECTRON SHIELD IS COMPRISED OF A PLURALITY OF SEGMENTS EACH SEGMENT HAVING ONE END WHICH IS CURVED TO CONFORM TO THE INSIDE CONTOUR OF THE ENVELOPE CORNER IN WHICH IT IS PLACED. THE OTHER END OF EACH SHIELD SEGMENT IS STRAIGHT AND SLIGHTLY OVERLAPS THE CURVED END OF THE PREVIOUSLY PLACED SEGMENT.

United States Patent inventors Gerald K. MacLean Hoffman Estates; Raymond J. Pekosh, Niles, Ill. App]. No. 21,744

Filed Mar. 23, 1970 Patented June 28, 1971 Assignee Zenith Radio Corporation SEGMENTED ELECTRON SHIELD FOR COLOR PICTURE TUBE References Cited UNITED STATES PATENTS 2,906,904 9/1959 Woughter et al. 313/85 3,404,303 10/1968 Levin 313/85 3,506,867 4/1970 Kraner 313/85 Primary Examiner-Roy Lake Assistant Examiner-V. Lafranchi Attorney-John J. Pederson ABTRACT= An electron shield for a shadow-mask-type of color tube bridges the space between the mask frame and the tube envelope. The electron shield is comprised of a plurality of segments each segment having one end which is curved to conform to the inside contour of the envelope corner in which it is placed. The other end of each shield segment is straight and slightly overlaps the curved end of the previously placed segment.

2 Claims, 5 Drawing Figs.

0.5. CI 313/85, 313/240 Int. Cl HOlj 1/53, H01 j 29/40 Field ofSeareh 313/85, 85 (S), 92 (B), 240

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\nventors Hlhw" Gerald K. Mac Leon R0 mond d. Pekosh r err c Attorney SEGMENTED ELECTRON SHIELD FOR COLOR PICTURE TUBE BACKGROUND OF THE INVENTION The present invention is directed to an improved electron shield for a color cathode-ray tube which features the use of a color selection electrode, such as a shadow mask.

It is well known that the forming of the phosphor screen of such a tube, which in the usual case is an interlaced pattern of three different phosphor materials, requires a great many process steps for some of which it is necessary that the shadow mask be in position adjacent the faceplate whereas for others the mask is removed. To permit such process steps to be con-- ducted, the envelope of the tube is constructed of a funnel section and a cap or faceplate panel section which is comprised of an image screen surrounded by a shallow peripheral flange. Studs projecting inwardly from the flange releasably receive mounting springs secured to the frame of the shadow mask and this frame has smaller overall dimensions than the faceplate panel. Accordingly, the mask may readily be installed and removed from the panel as required in carrying out the process steps through which the screen is deposited. The panel is then sealed to the funnel section of the envelope and the remaining steps are carried out to complete the tube.

From what has been said it is clear that a space surrounds the frame of the shadow mask, representing the separation of that structure from the envelope. Since it is common practice in the operation of a television receiver to overscan the screen, this space gives indiscriminate access of electrons to the screen which is undesirable; electrons should reach the screen only through the shadow mask or color selection electrode because only in this fashion is color purity obtained. Thus, it will be understood that electrons reaching the screen through the space between the frame of the shadow mask and the tube envelope result in spurious excitation of the peripheral portions of the screen and lead to degradation of color fidelity.

To overcome this difficulty, it has been proposed heretofore that a shield bridge the space between the frame of the shadow mask and the adjacent internal walls of the envelope. Usually the shield is formed of metal, such as relatively thin steel, but the arrangements previously adopted have been subject to two defects in particular. Notably, the shield structure is such that when it is placed into the generally rectangular panel section of the tube and secured to the mask frame, small gaps between the edge of the shield and the inner wall of the screen panel flange, or excessive pressure against the inner wall of the screen panel flange by the shield, may result because of the relatively large manufacturing tolerances typically encountered in the glass funnel and panel sections.

One solution to the problem has been to make the shield segments slightly larger than necessary. This method however is undesirable because excessive pressure is asserted against the inner wall of the glass panel section flange when the shield segments are forced into place and secured to the mask frame. This causes a condition whereby as the mask frame expands until the tube attains its operating temperature the edge of the shield is more likely to chip off flakes of the aluminized layer normally applied to the screen and frequently overlapping the flange of the screen panel. It is also more likely that the shield edge will dig into the bonding agent (usually a glass frit) which seals the panel and funnel sections, and dislodge small pieces of the frit. Both occurrences lead to undesired contaminants in the tube which may result on short circuits within the electron gun and destroy the tube.

Accordingly, it is an object of the invention to provide an electron shield for a color cathode-ray tube which avoids or minimizes the aforementioned difficulties of prior shield structurea.

It is a specific object of the invention to provide an improved electron shield for n shadow-musk type of three-gun color cathode-ray tube.

SUMMARY OF THE INVENTION The invention provides an electron shield for a color cathode-ray tube of the type having a glass envelope comprising a generally rectangular image screen panel section and a mating funnel section adapted to be sealed thereto, an interlaced pattern of different kinds of phosphor materials disposed on said screen, an electron gun means for developing at least one electron beam to be scanned across said screen, and a generally rectangular structural frame attached to said envelope hut spaced therefrom and supporting a color selection electrode across the beam path of said tube between said screen and said gun means to determine the particular phosphor material impinged by said beam during the scanning of said screen. An electron shield embodying the invention bridges the space between the frame of the color selection electrode and the tube envelope to provide substantially complete prevention of electron access to the image screen by way of such space notwithstanding the existence of relatively large manufacturing tolerances in the glass envelope sections. The shield is impervious to electrons and is composed of a plurality of segments each separately fixed to the mask frame and each having a curved portion conforming to and separately indexed to a single corner of the rectangular panel section.

BRIEF DESCRIPTION OF THE DRAWINGS The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings, in the several figures of which like reference numerals identify likelelements, and in which:

FIG. 1 is a crosssectional view of a shadow-mask type of color cathode-ray tube in which an electron shield embodying the invention has been installed;

FIG. 2 is a cross-sectional view, partially cut away, taken on line 2-2 ofFIG. 1;

FIG. 3 is a fragmentary cross-sectional view taken on line 3-3 of FIG. 2;

FIG. 4 is a fragmentary cross-sectional view taken on line 4-4 ofFIG. 2; and

FIG. 5 is a fragmentary cross-sectional view taken on line 5-5 of FIG. 2.

Referring now more particularly to FIG. I, the color cathode-ray tube there represented has an envelope compris ing a generally rectangular faceplate or panel section 10 and a mating funnel section 11. Envelope sections 10 and 11 must be matched as to configuration and dimensions in order that they may be integrated by the usual frit seal 12. The faceplate panel bears an interlaced pattern 13 of different kinds of phosphor materials, the more popular pattern being a multiplicity of so-called dot triads. Each triad consists of a dot of red phosphor, one of blue and one of green. Customarily the phosphor screen is backed by a layer of conductive and light reflecting material, such as aluminum, of such thickness as to be readily penetrated by the electrons of the electron beams of the tube. For convenience the aluminized layer has not been detailed in the drawing.

At the other end, the tube has the usual base 14 which accommodates the necessary pins through which connections are conveniently made to the electrode systems of the tube. These systems comprise a gun mount shown in block diagram 15 because its particular construction is of no particular concern to the present invention. Suflice it to say that the gun mount is an assembly or delta array of three electron guns which, when energized, develop three electron beams for scanning phosphor screen 13.

In order to obtain color selection, a color selection elec' trode l6, which for the case under consideration is an aperturetl nhudow mask. is disposed across the beam paths of the tube between screen l3 and gun mount l5. its function, as

well understood in the art, is to achieve color selection by permitting each of the three beams issued from gun mount R5 to see or impinge solely upon an assigned one of the different color phosphor materials of screen 13. Frequently this is referred to as defining red, blue, and green guns by which it is seen that each such gun energizes only the assigned color phosphor component of the screen. The color selection electrode is supported in position by a generally rectangular structural frame 17 of a shape corresponding to that of envelope panel section it). The mask frame 17 is removably secured within the tube envelope by studs projecting inwardly from the envelope to receive a plurality of mounting springs carried on the periphery of mask frame 17. One such stud i8 is shown in the drawing along with one of the mounting springs 19 but again all of this structure is well known.

As thus far described, there is nothing unique or unusual in the color tube of FIG. 1. it is the usual shadow mask device in which three electron beams, controlled by both chrominance and luminance information, are caused to scan the image screen 113 through the apertures of shadow mask 16. Through the assignment of the three beams with the three phosphor components of the screen, an image is reproduced in natural color. Clearly if in the scanning process the beams pass beyond the confines of mask 17, electrons may enter the space 20 between the mask frame and the envelope and cause spurious excitation of the screen as related above. This is avoided by an improved electron shield 21 arranged to bridge space 20 and preclude electron access to screen 13 through that space.

The details of the shield are best understood with reference to the view of FIG. 2. The shield is impervious to electrons, being formed, for example, of stainless steel of a thickness of approximately 3 mils. Electron shield 21 is composed of four segments, and each segment is individually fixed to mask frame 17, as for example by spot welding while in place in the image screen panel section 10. Each segment conforms to one comer and most of one side and is separately custom indexed to the particular panel unit with which it is to be finally assembled. One end of each segment is curved to conform to a corner of the panel section, while the other end conforms to one of the relatively straight sides of the generally rectangular panel section and terminates just short of the next corner so that it overlaps the curved end of the adjacent shield segment. After all four segments are in place, with the image screen panel section 110 serving as an indexing jig, the segments are separately spot welded or otherwise secured to mask frame 17. With this construction, it has been found that the peripheral shielding of overscanned and stray electrons is far superior to that obtained with prior shield constructions.

The present invention, therefore, provides effective electron shielding notwithstanding the relatively large glass manufacturing tolerances. Because each segment is independently fixed to mask frame 117 while being indexed to a single corner, minor dimensional variations from tube to tube are accommodated without undesirable gaps and without excessive pressure against the final anode coating or the frit seal.

FIGS. 3 and 4 show a detailed cross-sectional view of electron shield 21 in place and fixed to mask frame 117. Contact spring 22 is conventional and provides the electrical contact between mask frame 17 and inside envelope funnel wall 25 which is usually coated with graphite.

FIG. 5 shows cross-sectional view of the overlap of the curved end segment 23 and the uncurved end of the next segment 24. Preferably, the cross-sectional configuration of the shield 21 is as described and claimed in the copending application Ser. No. 737,968 of James L. Kraner, filed June 18, 1968, and assigned to the present assignee, which is now U.S. Pat. No. 3,506,867 granted Apr. 14, I970.

While a particular embodiment of the invention has been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and storage of the invention.

c claim:

ll. In a color cathode-ray tube of the type having a glass envelope comprising a generally rectangular image screen panel section and a mating funnel section adapted to be sealed thereto, an interlaced pattern of different kinds of phosphor materials disposed on said screen, an electron gun means for developing at least one electron beam to be scanned across said screen, and a generally rectangular structural frame attached to said envelope but spaced therefrom and supporting a color selection electrode across the beam path of said tube between said screen and said gun means to determine the particular phosphor material impinged by said beam during the scanning of said screen:

an improved electron shield bridging the space between said envelope and said frame to provide substantially complete prevention of electron access to said screen by way of said space notwithstanding the existence of relatively large manufacturing tolerances in said glass en velope sections, said shield being impervious to electrons and being composed of a plurality of segments each separately fixed to said frame and each having a curved portion conforming to and separately indexed to a single corner of said rectangular panel section.

2. An electron shield in accordance with claim 3, in which the shield is composed of four segments and in which the end opposite the curved portion of each segment is relatively straight and overlaps the curved end of the adjacent segment. 

